1. Field of the Invention
The present invention relates to apparatus and methods for the treatment of presbyopia using scanning and fiber-coupled lasers to ablate the sclera tissue.
2. Prior Art
Corneal reshaping, including a procedure called photorefractive keratectomy (PRK) and a new procedure called laser assisted in situ keratomileusis, or laser intrastroma keratomileusis (LASIK), has been performed by lasers in the ultraviolet (UV) wavelength of 193-213 nm. Commercial UV refractive lasers include ArF excimer lasers at 193 nm and other non-excimer, solid-state lasers, such as the one patented by the present inventor in 1992 (U.S. Pat. No. 5,144,630). Precise, stable corneal reshaping requires lasers with strong tissue absorption (or minimum penetration depth) such that the thermal damage zone is at a minimum (less than few microns). Furthermore, accuracy of the procedure of vision correction depends on the amount of tissue removed in each laser pulse, in the order of about 0.2 microns. Therefore, lasers at UV wavelengths between 193 and 213 nm and at the mid-infrared wavelengths between 2.8 and 3.2 microns are two attractive wavelength ranges which match the absorption peak of protein and water, respectively.
The above-described prior arts are however limited to the use of reshaping the corneal surface curvature for the correction of myopia and hyperopia. A variation of farsightedness that the existing laser surgery procedures will not treat is presbyopia, the gradual age related condition of suddenly fuzzy print and the necessity of reading glasses. When a person reaches a certain age (around 45), the eyes start to lose their capability to focus sharply for near vision. Presbyopia is not due to the cornea but comes about as the lens loses its ability to accommodate or focus sharply for near vision as a result of loss of elasticity that is inevitable as people age.
The present patent uses a xe2x80x9ccoldxe2x80x9d laser to remove sclera tissue (outside the limbus area) versus a xe2x80x9cthermalxe2x80x9d lasers in Sand""s patent (U.S. Pat. No. 5,484,432) to shrink the corneal shape (inside the limbus area). The cold laser of the present has a wavelength range of (0.15-0.36) microns and (2.6-3.2) microns which are also different from that of the xe2x80x9cthermalxe2x80x9d laser range of (1.80-2.55) microns proposed by Sand.
The prior arts of Ruitz (U.S. Pat. No. 5,533,997) and Lin (U.S. Pat. No. 5,520,679) are all limited to the corneal central portion and are designed to change the curvature of the cornea by ablation the surface layer of the cornea. The present patent, on the contrary, does not change the corneal central curvature and only ablating tissue outside the limbus.
The technique used in the prior art of Bille (U.S. Pat. No. 4,907,586) is specified to below conditions: (a) quasi-continuous laser having pulse duration less than 10 picoseconds and focused spot less than 10 micron diameter; (b) the laser is confined to the interior of a selected tissue to correct myopia, hyperopia or astigmatism, and (c) the laser is focused into the lens of an eye to prevent presbyopia. He also proposed to use laser to create a cavity within the corneal stroma to change its visco-elastic properties.
The xe2x80x9cpresbyopiaxe2x80x9d correction proposed by Ruitz using an excimer (ArF) laser also required the corneal surface to be reshaped to form xe2x80x9cmultifocalxe2x80x9d effort for a presbyopia patents to see near and far. However, Ruitz""s xe2x80x9cpresbyopiaxe2x80x9d correction is fundamentally different from that of the present patent which does not change the corneal curvature and only ablate the scleral tissue outside the limbus area. In the present patent, we propose that the presbyopia patent is corrected by increasing patient""s accommodation rather than reshaping the cornea into xe2x80x9cmultifocalxe2x80x9d.
To treat presbyopic patients, or the reversal of presbyopia, using the concept of expanding the sclera by mechanical devices has been proposed by Schachar in U.S. Pat. Nos. 5,489,299, 5,722,952, 5,465,737 and 5,354,331. These mechanical approaches have the drawbacks of complexity and are time consuming, costly and have potential side effects. To treat presbyopia, the Schachar U.S. Pat. Nos. 5,529,076 and 5,722,952 propose the use of heat or radiation on the corneal epithelium to arrest the growth of the crystalline lens and also propose the use of lasers to ablate portions of the thickness of the sclera. However, these prior arts do not present any details or practical methods or laser parameters for the presbyopic corrections. No clinical studies have been practiced to show the effectiveness of the proposed concepts. The concepts proposed in the Schachar patents regarding lasers suitable for ablating the sclera tissues were incorrect because he did not identify which lasers are xe2x80x9ccold lasersxe2x80x9d. Many of his proposed lasers are thermal lasers which will cause thermal burning of the cornea, rather than tissue ablation. Furthermore, the clinical issues, such as locations, patterns and depth of the sciera tissue removal were not indicated in these prior patents. In addition, it is essential to use a scanning laser to achieve the desired ablation pattern and to control the ablation depth on the sclera tissue. Schachar""s methods also require the weakening of the sclera and increase its diameter by expansion.
Another prior art proposed by Spencer Thornton (Chapter4, xe2x80x9cSurgey for hyperopia and presbyopiaxe2x80x9d, edot3d by Neal Sher (Williams and Wilkins, MD, 1997) is to use a diamond knife to incise radial cuts around the limbus areas. It requires a deep (90%-98%) cut of the sclera tissue in order to obtain accommodation of the lens. This method, however, involves a lot of bleeding and is difficult to control the depth of the cut which requires extensive surgeon""s skill.
Another drawback for presbyopia correction provided by the above-described non-laser methods is the major post-operative regression of about (30%-80%). And this regression is minimum in the laser method proposed in the present invention. The important concept proposed in the present invention is to support the post-operative results which show minimum regression. We proposed that the laser ablated sclera tissue xe2x80x9cgapxe2x80x9d will be filled in by the sub-conjunctival tissue within few days after the surgery. This filled in sub-conjunctival tissue is much more flexible than the original sclera tissue. Therefore the filled-in gap in the sclera area will cause the underlaying ciliary body to have more space to move. This in turn will allow the ciliary body to contract or expand the zonular fiber which is connected to the lens, when the presbyopic patient is adjusting his lens curvature to see near and far. The above described sub-conjunctival tissue filling effects and the increase of xe2x80x9cflexibilityxe2x80x9d of the sclera area are fundamentally different from the scleral xe2x80x9cexpansionxe2x80x9d (or weakening) concept proposed by the prior arts of Schachar and proposed by the implant of a scleral band. In the present invention, the laser ablated sclera area is not weakening, it becomes more flexible instead.
One objective of the present invention is to provide an apparatus and method to obviate these drawbacks in the above Schachar patents.
It is yet another objective of the present invention to use a scanning device such that the degree of ciliary mussel accommodation can be controlled by the location, size and shapes of the removed sclera tissue.
It is yet another objective of the present invention to define the non-thermal lasers for efficient tissue ablation.
It is yet another objective of the present invention to define the optimal laser parameters and the ablation patterns for best clinical outcome for presbyopia patients, where sclera ablation will increase the accommodation of the ciliary mussel by the increase of the flexibility in the laser-ablated areas.
It is yet another objective of the present invention to provide the appropriate scanning patterns which will cause effective ciliary body contraction and expansion on the zonules and the lens.
It is yet another objective of the present invention to provide a new mechanism which supports the clinical results of laser presbyopia correction with minimum regression. One important concept proposed in the present invention is to support the post-operative results which show minimum regression when presbyopia is corrected by a laser ablation for the sclera tissue.
We proposed that the laser ablated sclera tissue xe2x80x9cgapxe2x80x9d will be filled in by the sub-conjunctival tissue within few days after the surgery. This filled in sub-conjunctival tissue is much more flexible than the original sclera tissue. Therefore the filled-in gap in the sclera area will cause the underlaying ciliary body becomes more flexible. This will allow the ciliary body to contract or expand the zonular fiber connected to the lens when the presbyopic patient is adjusting his lens curvature to see near and far.
The concept presented in the present patent is to remove, by any methods including laser or non-laser methods, portion of the sclera tissue which is filled in by sub-conjunctival tissue to increase the flexibility of the scleral area and in turn causes the movement of the ciliary body and zonular fiber to increase the lens accommodation.
The preferred embodiments of the present surgical laser consists of a combination of an ablative-type laser and delivery unit. The ablative-type laser has a wavelength range of from 0.15 to 0.35 microns and from 2.6 to 3.2 microns and is operated in a pulsed mode such that the thermal damage of the corneal tissue is minimized.
It is yet another preferred embodiment of the present surgical laser to provide a scanning mechanism to effectively ablate the sclera tissue at a controlled depth by beam overlapping or by controlling the number of laser pulses acting on the sclera.
It is yet another embodiment of the present surgical laser to provide an integration system in which the ablative laser may be delivered by a scanner or by a fiber-coupled device which can be manually scanned over the cornea.
It is yet another embodiment of the present surgical laser to focus the laser beams to generate the sclera ablation patterns in radial lines, curved lines, dotted rings, or a slit pattern.
It is yet another embodiment of the present surgical laser to provide an integration system in which the sclera ablation leads to the increase of the accommodation of the ciliary muscle for the treatment of presbyopia and the prevention of open angle glaucoma.
It is yet another preferred embodiment of the present application to provide a non-laser mechanical method including a diamond knife to remove a portion of the scleral tissue and cause the movement of the ciliary body for lens accommodation.
Further preferred embodiments of the present surgical laser will become apparent from the description of the invention which follows.